How do I find my iPhone if my find my location is off?

See the following from If Find My iPhone or Find My iPad isn't enabled on your missing device - Apple Support

If your missing device doesn't appear in the Find My app or at iCloud.com/find, you didn't turn on Find My. There's no other Apple service that can find, track, or flag your device for you. But there are steps that you can take to help protect your data.

As noted, that support article has other steps that you may want to take.

If Find My is off on the iPhone, then you will have to look for the phone the old fashioned way.....with your eyes.